1. Field of the Invention
This invention relates to a specific terminal-modified imide oligomer which is soluble in various organic polar solvents, has a relatively low melting point and further has a terminal group (i.e., end group) capable of undergoing addition polymerization (i.e., cross-linking reaction) and an imide main chain bond, and a solution composition of said oligomer.
The terminal-modified imide oligomer or the solution composition of the oligomer can be widely employed, for example, as a matrix resin which is used for the preparation of a composite material containing a variety of fillers, reinforcing agents and heat-resistant adhesives for adhering various materials, or a starting material for the preparation of various heat-cured products. The products obtained by curing the imide oligomer of the invention are prominently high in heat resistance.
2. Description of Prior Art
Polyimide resins of a low molecular weight have been heretofore employed as matrix resins of various molded products or fiber-reinforced composite materials, because they show high heat resistance.
However, the known polyimide resins (specifically, aromatic polyimides) are generally low in solubility in organic solvents, so that they have been used in the form of a solution of polyamic acid, that is a polyimide precursor, for various purposes. Since the polyamic acid is a condensation polymer, there arise various problems for removing gases such as water (i.e., reaction water) which is produced in the curing process of a polymer in the preparation of products.
In view of those problems, there has been recently proposed, for example, a polyimide resin of addition type having an unsaturated terminal group (i.e., end group) which is produced by a reaction of (a) an aromatic tetracarboxylic dianhydride such as pyromellitic dianhydride and benzophenonetetracarboxylic dianhydride, (b) an aromatic diamine and (c) an unsaturated reactive compound, as described in Japanese Patent Provisional Publications No. 59(1984)-167569, No. 60(1985)-250030, No. 60(1985)-260624, No. 60(1985)-260625, No. 61(1986)-247733, No. 62(1987)-29584, etc.
However, the above-mentioned known polyimide resins also have various drawbacks. For example, a specific diamine compound which is expensive and not easily obtainable should be used in the preparation of the polyimide resins, or the resulting polymer is not always high in solubility in an organic solvent. Otherwise, a specific organic solvent having a high boiling point is required in the preparation of a polyimide solution. In addition, a melting point of the obtained polyimide resin becomes too high, whereby the quality of a product deteriorates in the preparation from the polyimide resin.
More specifically, when a solution which contains a polyimide of high melting point in a low concentration is impregnated into reinforced fibers to produce a composite material, the impregnation of the solution into the reinforced fibers should be repeated several times to obtain the desired resin content, or the molding process should be carried out at an elevated temperature. Further, when a polyimide solution obtained by utilizing the aforementioned known solvent of a high boiling point is used as an adhesive, it is difficult to completely evaporate the high-boiling solvent, and as a result, the polyimide solution is unsuitable for practical use because it shows poor adhesiveness.